The manner in which a video signal is quantized determines the bit rate of the encoded signal and the quality of the image reconstructed from that encoded signal. Perhaps most significant in this context is the quantization step size, which is derived from a predetermined mapping of the so-called quantization parameters and which directly controls the coarseness/fineness of the quantization employed in developing the encoded signal. Therefore, in order to achieve the maximum picture quality for a particular predetermined target bit rate, the quantization parameters need to be appropriately selected.
Prior approaches to selecting the quantization parameters have been statistically based, have required computations necessitating that the entire image or portions thereof be processed multiple times, or have employed models of the human visual system. These prior approaches are complex, require large amounts of memory or introduce large delays. Moreover, such prior solutions typically ignore the nature of non-homogeneous regions of an image, such as edges. Furthermore, none of the prior solutions employs a single quantization parameter in an effective manner. A single quantization parameter is in fact required, however, by the video coding syntax of the Motion Picture Expert Group (MPEG), as set forth in the International Standards Organization (ISO) standard Committee Draft 11172-2.